The present invention relates to a coupling for passages of a fluid such as a gas.
In general, a coupling comprises a socket and a plug connected thereto. A conventional coupling is disclosed in Japanese Utility Model Publication No. Sho 53-2811. In this prior art, an annular valve seat B is disposed in a socket A, and a hollow cylindrical valve body D whose rear end is blind is inserted in the valve seat B so as to be axially slidable, as shown in FIG. 1. A plurality of communication bores C are circumferentially formed in the central portion of the wall of the valve body D. Further, a stepped annular packing F in which a conical metal ring E is embedded is fixedly inserted at its step portion in the valve seat B. When a plug G is inserted into the socket A so as to allow the fluid flow therethrough, the outer circumferential surface of the plug G is brought into contact with the inner circumferential surface of the packing F. The inner end of the valve body D is normally biased by a coil spring H to close the coupling. An O-ring K is disposed at the outer circumference of the front end of the valve body D. When the valve body D is closed, the O-ring K is in contact with the inner edge of a flange L of the valve seat B which faces inward so as to effect sealing between the flange L and the valve body D.
In the conventional coupling of this type, the communication bores C are located in the valve seat B when the valve body D is closed, as shown in FIG. 1. When the plug G is inserted into the socket A, the communication bores C are located outside the valve seat B, and the interior of the socket A communicates with that of the plug G. Therefore, when the plug G is inserted into the socket A in order to allow a fluid such as gas to flow, the flange L is removed from the O-ring K before the communication holes C are exposed to the interior of the socket A. The fluid in the socket A may flow into a gap between the inner edge of the flange L and the outer peripheral wall of the valve body D and then into a space between the packing F and the valve body D. Thereafter, the fluid may leak a gap between the rear end of the socket A and the rear end of the plug G to the outside of the coupling.
When the plug G is inserted into the socket A to open the coupling, the socket A is sealed from the plug G by only one packing F, resulting in insufficient seal.
When the valve body D is opened or closed, the valve body D must be moved beyond the inner edge of the flange L. For a quick operation, the stroke of the valve body D is required to be shortened. This necessitates the flanged portion of the valve seat B to be very thin. The valve seat B supports the valve body D at a very short width, resulting in an unstable supporting, thus preventing smooth movement of the valve body D when it is opened and closed.